This invention relates generally to transmissions for varying the output torque of engines and, preferably, to an automotive transmission of the type in which the torque and speed of an engine drive can be continuously and infinitely varied from vehicle start-up through normal highway driving.
All commercial automotive transmissions are large, complex, and wasteful of fuel and, particularly when used with diesel engines, cause serious problems in air pollution. The relative inefficiency of commercial automatic transmissions, with their torque converters, has made them a principal object for needed improvement for more than 60 years. The prior art is replete with variations of multiple planetary and orbital gearing concepts for automatic automotive transmissions in which output speed is continuously varied serially through each of a plurality of stepped gear ratios.
When a vehicle such as a loaded truck begins to accelerate (e.g., from a standing stop), the speed of the engine drive changes repetitively as it moves the vehicle""s conventional transmission (either manual or automatic) through successive gear changes. Each such repetitive speed change results in the inefficient discharge of unburned fuel and, particularly with diesel engines, the generation of undesirable and unhealthy pollutants. Therefore, many new transmission designs are being suggested and tried in the hope of finding some way to increase engine efficiency and reduce pollutants. Among these designs are proposals for infinitely variable transmissions incorporating input and output drive cones or toroidal surfaces (as distinguished from gears) being connected by drive belts or by a lubricant that increases frictional traction between the elements. The former are limited to relatively small vehicles, while the latter have not as yet achieved any commercial success.
Fairly recently, a new continuously and infinitely variable automotive transmission (xe2x80x9cIVTxe2x80x9d) was disclosed in U.S. Pat. No. 5,186,692 (Gleasman et al.). This just-cited Gleasman IVT connects an engine drive to an output shaft by an orbital drive (similar to that used by Henry Ford in the Model T), and it infinitely varies gear ratios by controlling the rotation of a control gear in the orbiter with a separate hydraulic control motor actuated by a hydraulic pump. This just-cited Gleasman IVT is also smaller and lighter than commercial transmissions, and an experimental model was successfully tested using hydraulics to rotate the control gear of the orbital drive.
However, during the development of a commercial prototype for this just-cited Gleasman IVT, we suddenly realized that a significant improvement could be made by modifying the mechanism in a manner similar to new technology we had very recently developed in another automotive area, namely, the design of steer-drives for tracked vehicles. In one known group of steer-drives, a combination of two identical differentials is used to divide engine driving torque received from the output shaft of the vehicle""s conventional transmission. (For instance, see U.S. Pat. No. 1,984,830 (Higley) and U.S. Pat. No. 5,390,751 (Puetz et al.).) In this type of steer-drive, the two identical differentials divide the driving torque into two individual drives, one for each track (or for each oversized wheel) of a large off-road vehicle. In our recent improvement to this known group of steer-drives, disclosed in U.S. Pat. No. 6,342,021 (Gleasman et al.), a pair of identical orbiters replaces the two differentials in a steer-drive that makes it possible to steer a tracked vehicle at highway speeds with a conventional steering wheel.
The above-identified Gleasman IVT, which is improved by the invention disclosed herein, has relatively small physical proportions and can be scaled up or down for use in smaller vehicles as well as large semi-trucks. Also, the tests of our earlier experimental prototype (referred to above) indicate that this IVT should significantly reduce the pollutants emanating from a diesel engine combined with this IVT.
The improved transmission disclosed herein incorporates the general format of the two identical orbiter differentials disclosed in our just-cited steer-drive patent. However, in this improvement, only a single orbiter is used in a new combination that includes a relatively minor but significant change that, if heretofore appreciated, could have been made to Ford""s Model T transmission over 90 years ago. This minor change not only simplifies the orbiter mechanism of the IVT but, for automotive uses, provides a remarkable increase in efficiency and an even further reduction in size and weight.
The key element of this improved transmission is only a single, remarkably simple, minimal orbiter. Namely, an input gear and an output gear, being connected, respectively, to separate input and output shafts, are both mounted along the same first axis and interconnected through a cluster gear that meshes with only the input and output gears. The cluster gear is mounted for rotation on an orbit shaft that is positioned parallel with the first axis and carried by a web that is itself mounted for rotation about the first axis. The orbit shaft and the cluster gear orbit, respectively, both the first axis and the input and output gears.
The orbiting web of this minimal gear arrangement is connected to a control motor so that: (a) if the control motor prevents rotation of the orbiter web, the output gear rotates directly with the input drive but solely at a predetermined reduction of the input drive; (b) if the control motor is rotated in a first (xe2x80x9cforwardxe2x80x9d) direction, the predetermined reduction of the output gear relative to the input drive is diminished proportional to the speed that the control motor rotates the web; (c) if the control motor is rotated in the opposite (xe2x80x9crearwardxe2x80x9d) direction at a predetermined relatively slow speed, the output gear comes to a stop, in effect providing a xe2x80x9cgeared neutralxe2x80x9d in which torque is applied to the web to hold the vehicle in a stopped position for start-up and when stopping in traffic; and (d) finally, when the vehicle reaches highway speeds, the control motor is disconnected from the orbiter web which is then connected with the input drive shaft through a predetermined overdrive gear ratio that causes the transmission to rotate the output drive shaft faster than the engine drive by the predetermined overdrive.
This just-mentioned overdrive is located between the engine drive and the transmission rather than being conventionally positioned between the transmission and the final output shaft. Therefore, the overdrive of the invention is subjected only to engine torque rather than being subjected to the higher torque generated by the gear reductions of the transmission. Thus, the overdrive of the invention can be made substantially smaller and lighter, providing further reductions in weight and size when compared to conventional transmissions.
However, in regard to the just-mentioned xe2x80x9cgeared neutralxe2x80x9d condition, working with experimental models has revealed a surprising and potentially valuable feature of this novel orbiter improvement: We have learned that, if the control motor is xe2x80x9cneutralizedxe2x80x9d (e.g., by disengaging a clutch) when the engine drive is idling, the idling-speed rotation of the input gear will cause the cluster gear to rotate the web in the opposite direction at a speed that automatically causes the output gear to come to a stop. This automatically provides the required zero-speed automatic xe2x80x9cneutralxe2x80x9d for start-up and for stopping in traffic without necessitating a programmed application of reverse torque to create the required predetermined speed reversal of the web.
The many possible ramifications of this latter feature have as yet not been fully appreciated. However, the preferred hydraulic pump/motor embodiment of the invention includes a valve-regulated xe2x80x9cby-passxe2x80x9d in the closed-loop hydraulic circuitry shared by the pump/motor combination that permits the control motor to be reversed by the idling speed rotation of the input gear without disengaging the first clutch.
For highway use, this improved transmission uses only a few overdrive gears in addition to the minimal functional gearing included in its single orbiter. However, persons skilled in the art will appreciate that the minimal orbital transmission of the invention can be bolstered to meet increased torque loads, without changing the gear reduction ratio provided by the web-mounted cluster gear, by the addition of one, two, or three identical cluster gears carried on the same web.
Also disclosed are (a) an optional additional known gear reduction (e.g., for large truck start-up), (b) utilization of the above-mentioned valve-regulated xe2x80x9cby-passxe2x80x9d in the closed-loop hydraulic circuitry as a safety device for preventing pressure overload in the closed loop hydraulic fluid circuit connecting the hydraulic pump and motor, and (c) a power takeoff.